The invention is based on a wiper strip for windshield wipers.
Known windshield wipers comprise a wiper arm constructed out of a mounting part and a hinged part with a wiper bar hinge-mounted on the mounting part via a hinged joint. A hook-shaped end of the wiper bar usually grips in a hinging compartment of a wiper blade that is formed by two lateral supports of a center strap, and encloses a pivot pin. The joint designed in this fashion guides the wiper blade over the vehicle window during the swivelling movement.
The wiper blade consists of a multisectional carrying strap system with secondary straps hinge-mounted on the center strap, of which at least a few hold a wiper strip by means of claws on their ends. The long wiper strip is made of rubber and has a profile having two main sections: a profile spine, and a functional part. The wiper strip is connected to the carrying strap system at the profile spine and, in fact, by the claws of the claw straps gripping in opposing longitudinal grooves of the profile spine. In so doing, the claws enclose a part of the profile spine that comprises at least one further longitudinal groove in which a spring is housed. If two springs are used, they lie symmetrically arranged in opposing longitudinal grooves. Wiper blades are also known in which a spring is provided in a centrical longitudinal channel of the profile spine. During operation, the springs should evenly distribute a bearing force directed toward the wiper blade across the entire length of the wiper strip and stiffen it at the same time.
The profile spine is connected to the functional part of the wiper stripxe2x80x94which comprises a wiper wedge and a wiper lipxe2x80x94via a thin bridge piece. The cross-section of the wiper wedge has the shape of a nearly isosceles triangle, the base side of which points toward the connecting bridge piece, while the wiper lip is integrally moulded on the tip. During wiping, the wiper blade is loaded in the direction toward the vehicle window by means of the bearing force, and the wiper lip bears against the vehicle window. Additionally, a force created by the swivelling movement acts transversely on the rubber profile. While the profile spine is moved by the side force, the wiper lip remains in its position at first. The thin bridge piece between the profile spine and the functional part thereby acts as a tilting joint due to its high elastic deformability, so that the wiper lip on the functional part more or less takes on a pitch of 45xc2x0 in relation to the glass surface. This dragged position is the working position of the wiper lip. In this position, the wiper wedge is tipped over so far that its outside top shoulder touches the underside of the profile spine.
As a result of the oscillating wiping motion of the windshield wiper, reversal points result in the end positions of the motion. Here, the wiper wedge folds over in the opposite direction and then assumes a dragged working position once more. This process of folding over produces an unpleasant noise in traditional windshield wipers. Additionally, the wiper rubber is elastically deformed to a great extent in the region of the tilting bridge piece. Over the course of service, this leads to a permanent deformation of the wiper rubber profile, which only impairs the wiper function of the windshield wiper at first, but eventually even prevents the folding-over action.
A wiper strip is made known in DE 91 04 461.8 U1 in which a damping strip is provided between the profile spine and the striking shoulder of the wiper wedge. When the functional part of the wiper strip folds over at the reversal point, the shoulder first strikes against the damping strip and pushes it until it comes to rest against the profile spine. As a result, the striking velocity is decelerated, and the noise produced during the folding-over action is quieted. An acute angle xcex1 between the damping strip and the profile spine, the tip of which points toward the tilting bridge piece, also causes the damping resistance to increase as the deformation of the damping strip increases. The damping strip prevents the angle of attack of the wiper lip in relation to the vehicle window from being reduced, so that the alternate bending load of the tilting bridge piece is unchanged.
According to the invention, the functional part of a wiper strip includes a supporting section that is connected to the profile spine via a first tilting bridge piece and to the wiper wedge via a second tilting bridge piece. The cross-section of the supporting section has the shape of an isosceles trapezoid, the base side of which points towards the first tilting bridge piece. The supporting section therefore follows a basic shaping of the functional part, which has its greatest width on the side facing the first tilting bridge piece and decreases continuously toward the exposed end of the wiper lip.
During operation, the functional part tilts in a first action to the side until a top shoulder of the supporting section touches the underside of the profile spine. The wiper lip is now tilted only at a first partial tilt angle. As the movement progresses, the wiper wedge tilts to the side until its top shoulder touches the underside of the supporting region. Only now does the wiper lip have a necessary tilt angle of nearly 45xc2x0 in relation to the vehicle window. According to the invention, the working position of the wiper lip is reached in two actions that take place at different times. The advantage of this procedure is a dampened folding-over of the functional part of the wiper strip at the reversal points of the swivelling movement combined with a greatly diminished folding-over noise.
A further advantage of this profile design also lies in the fact that an optimal relationship exists between geometric folding-over and elastic deformation, in that the entire tilt angle is distributed over the two tilting bridge pieces and, therefore, the deformation of the functional section associated with this is distributed over the two tilting bridge pieces, so that each tilting bridge piece is loaded with only a part of the alternate bending load. Localized stress overloads that occur in traditional wiper strips having only one tilting bridge piece do not occur here. Moreover, undercuts that expand the height of the open space between the lower edge of the profile spine and the base surface of the trapezoidal supporting section toward the tilting bridge piece reduce the elastic deformability of the first tilting bridge piece. According to the invention, further undercuts are also provided in the open spaces between the supporting section and the wiper wedge. The tilting behavior of the tilting bridge pieces can be coordinated with each other by means of the shaping of the open spaces and undercuts, and preferably in such a fashion that the first tilting bridge piece repeatedly participates in the tilting motion, while the tilting motion of the second tilting bridge piece largely does not take place until the supporting section is already resting against the profile spine.
A reduced elastic deformation favorably affects the life of the wiper rubber and prevents a permanent deformation of the wiper profile from occurring as a result of high elastic deformation over the course of service. The embodiment of the profile spine remains largely unaffected by the design of the functional section according to the invention, so that such wiper rubber profiles can be used in wiper blades with the most diverse claw shapes and in xe2x80x9cunarticulatedxe2x80x9d wiper blades.